Influence of extracellular polymers on electrokinetic properties of heterotrophic bacterial cells examined by soft particle electrophoresis theory

Abstract

In this study, influence of extracellular polymeric substance (EPS) on the bacterial electrokinetics and cell adhesion to glass beads was examined for four kinds of heterotrophic bacteria (A1, A2, B1 and B2 strains) isolated from a biological reactor treating domestic wastewater. Electrophoretic mobility data were analyzed by Ohshima's soft particle theory. Cell adhesion to glass beads was carried out by packed-bed method, and the data were interpreted as the cell collision efficiency. Electrophoretic mobility measurements showed that all four strains had soft particle characters. EPS covering on cell surface increased the softness of the cell surface and decreased the negative surface charge density around the cell surface. For A1, A2 and B1 strains, both surface potential based on soft particle theory Ψ0 and conventional zeta potential ζ of intact were lower than those of washed cells. While ζ increased from −31.6 to −27.2 mV when EPS was removed, Ψ0 estimated from soft particle altered from −11.0 to −14.9 mV in the case of B2 strain, indicating EPS covering resulted in the increase of cell surface potential. Cell collision efficiencies are in qualitative agreement with the result of the cell surface potential evaluation based on soft particle analysis.